Field of the Invention
The present invention relates to a solenoid controlled valve to be used as an inlet valve in an antilock brake control apparatus for a vehicle.
An antilock brake control apparatus controls the fluid pressures to be applied upon a wheel cylinder in accordance with the skid status or the like of a wheel. Various controlling valves have been proposed for controlling such fluid pressure.
For example, Japanese Patent Publication No. 49-28307 discloses an antilock brake control apparatus as shown in FIG. 1. An inlet valve 4 composed of a normally open on/off type solenoid controlled valve is interposed in a main path 3 communicating a master cylinder 1 with a wheel cylinder 2. A discharge valve 8 composed of a normally closed on/off type solenoid controlled valve is interposed in a return path 7 returning from the wheel cylinder 2 to the main path 3 through a reservoir 5 and a pump 6.
The antilock brake control apparatus has three-type modes in the fluid pressure control during an antilock controlling time. Opening the discharge valve 8 and closing the inlet valve 4, working fluid within the wheel cylinder 2 is exhausted to the reservoir 5 (depressurizing mode). Closing the inlet valve 4 and the discharge valve 8, and the fluid pressure within the wheel cylinder 2 is held (holding mode). Closing the discharge valve 8 and opening the inlet valve 4, the fluid pressure within the wheel cylinder 2 is increased (pressurizing mode).
Japanese Patent Publication No. 5-65387 by the present applicant discloses, as shown in FIG. 2, an antilock brake control apparatus having an inlet valve 11 and a discharge valve 12. The inlet valve 11 and the discharge valve 12 are integrated with each other. The inlet valve 11 interposed in a main path 3 is a non-solenoid controlled type flow amount control valve. The discharge valve 12 interposed in the return path 7 is a normally closed on/off type solenoid controlled valve.
A similar configuration antilock brake control apparatus is described in WO95/09098 or the like.
The inlet valve 11 composed of a flow amount controlling valve has a sleeve 15 comprising a port 15a communicated with the master cylinder 1, ports 15b and 15c communicated with the wheel cylinder 2, and a port 15d communicated with the discharge valve 12. A spool 16 is accommodated slidably within the sleeve 15. A stationary orifice 17 is provided in an inlet path 16a passing in an axial direction through the spool 16. The spool 16 has a radially extending fluid passages 16b, 16c and 16d for communicating the inlet path 16a and the ports 15a through 15c. Further, the spool 16 is urged upwardly in the drawing by a spring 18. The discharge valve 12 which is the normally closed on/off type solenoid controlled valve has a movable core 21 in a valve body 20. The valve body 20 can be seated on a valve seat 19. When a coil 22 is energized, the valve body 20 moves downward in the drawing to open.
This type of antilock brake control apparatus has two-type modes in the fluid pressure control during the antilock controlling time. Namely, opening the discharge valve 12, the depressurizing mode is provided where the working fluid of the wheel cylinder 2 is exhausted into the reservoir 5. Closing the discharge valve 12, the pressurizing mode is provided where the fluid pressure within the wheel cylinder 2 is increased.
But, in the case that both the inlet valve 4 and the discharge valve 8 are on/off type solenoid controlled valves as shown in the FIG. 1, pressure increasing per unit time (pressurizing rate) becomes larger when the fluid pressure difference between the master cylinder 1 and the wheel cylinder 2 is large, even if the execution time of the pressurizing mode is the same, and the pressurizing rate becomes smaller when the fluid pressure difference is smaller. When the pressurizing rate during the pressurizing mode depends upon the fluid pressure difference between the master cylinder 1 and the wheel cylinder 2, it is difficult to control the fluid pressure with high accuracy.
Namely, as shown in FIG. 3(A), when a locking symptom is detected with the difference between a car body speed and a wheel speed becomes larger at a time t1, the depressurizing mode is carried out (time t1 through t2), and a holding mode is carried out (time t2 through t3) when the wheel speed is recovered. When the wheel speed is further recovered, the pressurizing mode (time t3 through t4) and the holding mode are alternately repeated (pressurizing/holding mode) to slowly increase the fluid pressure within the wheel cylinder 2 (time t3 through t5). When the wheel speed is further recovered, the pressurizing mode is carried out (time t3 through t4). As the difference between the vehicle speed and the wheel speed becomes immediately higher again due to the high pressurizing rate in this case, it becomes necessary to carry out the depressurizing mode. Thus, it is necessary to repeat the pressurizing/holding mode and the depressurizing mode at a short period. A period from the lock symptom produced to the next lock symptom produced (skid cycle) is short.
In the case that an inlet valve 11 is a non-solenoid controlled type flow amount controlling valve and the discharge valve 12 is a normally closed on/off type solenoid controlled valve as shown in FIG. 2, a spool 16 moves vertically due to the balance between a force applied upon a spool 16 by the fluid pressure difference before and after the stationary orifice 17 and the force of the spring 18 at the pressurizing mode. A variable orifice is composed by the repeated communication and interruption between the port 15a and the fluid passage 16b. Thus, the pressurizing rate during the pressurizing mode is constant independently of the fluid pressure difference between the master cylinder 1 and the wheel cylinder 2, and the pressurizing rate is small (slow pressurizing). In this terms, the flow amount control type inlet valve 11 is advantageous in the fluid pressure control. But the antilock brake control apparatus of FIG. 2 can not make the fluid pressure overshoot small, because the apparatus cannot carry out the holding mode.
When the wheel speed is recovered by the pressure decreasing within the wheel cylinder 2 in a depressurizing mode (time t1 through t2) after the locking symptom has been detected as shown in FIG. 3(B), the pressurizing mode is immediately carried out (time t2 through t3) . When the pressurizing mode is only carried out without execution of the holding mode in this manner, the fluid pressure of the wheel cylinder 3 is increased more than necessary (fluid pressure overshoot), and the locking symptom is detected again (time t3) . As the result, the skid cycle in this case becomes much shorter than the skid cycle in the case that both the inlet valve 4 and the discharge valve 8 are an on/off type solenoid controlled valve. A locking symptom is apt to be caused by the fluid pressure overshoot, thereby the depressurizing mode is necessary to be carried out frequently. Thus, the total pressure reduction of one antilock controlling is large. As this reason, the pump 6 for pumping a working fluid from the reservoir 5 to the master cylinder 1 bears large load. Consequently, the pump 6 is necessary to be higher in pumping performance.